Hybrid FSO/RF Communications System for High-Availability, High-Capacity Networks

Free-space optical communications (FSO) systems have gained increasing interest for both defense and commercial applications due to their ability to provide secure, long-distance, high-capacity communications on the move. In terrestrial environments, because clouds and strong weather effects can limit FSO systems performance, integrating them with directional radio frequency (RF) links can yield a system that leverages the best of both modalities - the high capacity of FSO when available with the reliability of the RF link to ensure the highest priority data can be sent even during degraded weather conditions. This paper will present the development of a highly integrated FSO/RF link architecture implementing three key functionalities: (1) operation at data transfer rates up to 10 Gbps, (2) seamless failovers between the FSO and RF modalities, and (2) the necessary quality of service (QoS) mechanisms to handle the rate disparity between the two links while providing priority to critical data. This architecture utilizes a network transport system that provides layer 2 data transport and QoS arbitration across the FSO and RF modalities. Results from testing in lab as well as at outdoor ranges of up to 30 km will be presented.